The distillation of solvents has become very important due to the increasing cost of solvents and the problems of disposing of hazardous wastes. Distillation technology has been used for some time but never designed safely for the small application. The basic reason such units were not available for small usages was that all available designs were far too costly and unsafe when made in small units. Underwriter's Laboratories (UL), in their book #UL823 entitled Electric Heaters for Use in Hazardous Locations, states on page 16, "The maximum acceptable temperature for the external surface of the heater for Class 1, Group D shall be 365.degree. F." This is by far the most important safety design aspect of the small still revealed herein. The very thick cast bottom of this vessel and the cast-in thermowells with redundant temperature controllers prevent the temperature from exceeding 365.degree. F. at any point on the inner surface.
Materials to be distilled frequently involve organic compounds which may be explosive. One criteria to carry out the process of the present invention is to prevent the temperature at any point on the inside periphery of the boiling vessel from exceeding the auto ignition temperature of the compound even during mal-operation and thus result in explosion of such organics; the hottest spot to which the liquid is exposed must be below the auto ignition temperature of the material being distilled. For example, the auto ignition temperature of Heptane is 450.degree. F. Underwriter's Laboratories states that for most common organic solvents, the lowest auto ignition temperature is 365.degree. F. Thus for the practical case of common organic solvents, the lowest auto ignition temperature is 365.degree. F. As stated for safe operation the temperature of the hottest spot with no exceptions must be below the auto ignition temperature of the compound being distilled even in serious mal-operation.